Of these 2, I'd say it's very close. Assuming Platinum for both and the top week for each under that category, I'd say GV will trade a little better than GC. Both areas and resorts are easy trades and along with Williamsburg and Branson, all overbuilt compared to demand. GC might have slightly lower fees though I doubt they'll be much different over time. The other big differences to me are that GC has a broader Platinum season and that GV reservations start on Thursday. This last point can be a big difference in some case, esp if you have other Marriott ownerships now or in the future. As for getting to HH and MB for summer using them I'd say those are tough trades. Both will likely get you there if you're flexible (entire school break), for HH it'll be easier if you list all resorts not just the top ones there. I think the FL club is a draw for GV as well. Both have lockoff's
Personally from a trading standpoint I see GV have a mildly better trade power, FL club option and the Thursday start date for reservations. Side by side and with no other reason to chose GC, I'd go with GV hands down. I'd go with GC over GV gold. If you live close enough to either to use periodically, that might make a difference.
Other considerations would be a 3 BR at each location, EOY at more than one location, CA desert Gold, Willow Ridge Platinum, Manor Club sequel and Harbour Lakes Platinum plus some of the non lockoff locations. Further discussion on those points: a 3 BR likely isn't worth it for your stated purpose because it's unlikely you could trade to a 3 BR other places so you wouldn't deposit as a 3 BR and the fees are actually as or more expensive when you compare deposits. But if you'll use a 3 BR at times when you actually use it and you can find one at a good price, that could be a consideration. You could potentially get more than one EOY and give you more options for around the same price, say an EOY at each of the 2 locations you're looking for or an EOY at one of these for exchanging plus something to use part or all the time. HL, MC sequel & WR will likely be around the same or a little less in fees and possible less to buy. The trade power will be around the same as the 2 resorts in question with WR being basically identical to GC then HL and GV will trade on the same trade power since II does more community rating for trade power. They will have slightly lower resort quality ratings which could be enough to make a difference for HH (top resorts) & MB. But both are likely easier to buy at a bargain. I recently bought a HL 2 BR annual Platinum week for under $1K with seller paying closing and I got this years week for free which I locked off and deposited. I've had 2 GV weeks ROFRed in the last year. CA desert gold will likely trade as well as GV and as good or possibly better than GC with similar resort ratings. Fees will be higher but DS I is the only one in discussion that doesn't have the ROFR option for Marriott.
I'd also consider the potential of a non lockoff option. With the upgrade fee now and the lockoff fee to Marriott plus the addition exchange fees, the L/O is not as big a benefit as it once was. Off the top of my head (likely will miss one) and used strictly for trading, I'd list Legend's Edge, Doral, NJ, Cypress Harbour, Grande Ocean Gold (not other HH gold options), Harbour Point summer week (lowest resort rating), and Manor Club (original) as possible considerations. If you're always wanting a 2 BR I think this is viable. You might also look at Trust points, more to get into but you wouldn't have the II and lockoff fees extra and you'd have more choices. Personally if I were starting out today with the current set up and knowing what I know, I'd likely not do trust points (or some type of direct Hybrid purchase) in this situation but both are consideration.
It sounds like this may be your first timeshare purchase or at least first Marriott. If that's the case I'd suggest you consider something that might be less of a trade value but something you'll use routinely. We own both using weeks and trading weeks, unfortunately there's often not a lot of crossover in a general sense but your location and vacation preferences might make a few resorts stand out. Buying just to trade can be the best value in some cases but it has risk.
